Gasanov N.
phd in physics, associate professor, leading researcher at the Institute of Physics of the Ministry of Science and Education of Azerbaijan
Khallokov F.
phd in physics, Head of the Department of Biophysics and Information Technology in Medicine, Bukhara Medical Institute named after Abu Ali ibn Sino, Bukhara, Uzbekistan
Ismailova P.
phd in physics, associate professor, head of laboratory at the Institute of Physics of the Ministry of Science and Education of Azerbaijan
Umarov S.
doctor of physical sciences, professor of the Department of Biophysics and information technology in medicine, Bukhara Medical Institute named after Abu Ali ibn Sino, Bukhara, Uzbekistan
Hadjiyeva A.
researcher at the Institute of Physics of the Ministry of Science and Education of Azerbaijan
Huseynova K.
phd in physics, teacher of the department “Physics and its Teaching Methodology”, Sumgayit State University, Sumgayit, Azerbaijan

Abstract
The effect of partial substitution of indium atoms by ytterbium atoms (0.5 and 1 mol%) on the band gap of TlInS₂ single crystals irradiated with electrons with an energy of 2 MeV and a fluence of up to 1·10¹⁶ el/cm² has been studied. The band gap from the measured absorption spectra at room temperature was determined using the Tauc method. It was found that electron irradiation leads to a decrease in the band gap in all TlIn_1-xYb_xS₂ crystals studied. In the range of 77–200 K, the temperature dependence of the exciton absorption band in TlInS₂ and TlIn_0.995Yb_0.005S₂ single crystals was studied.

Keywords: semiconductor, rare earth element, exciton, band gap, electron irradiation.